Method of patterning a metal gate of semiconductor device

ABSTRACT

Provided are methods of patterning metal gate structures including a high-k gate dielectric. In an embodiment, a soluble hard mask layer may be used to provide a masking element to pattern a metal gate. The soluble hard mask layer may be removed from the substrate by water or a photoresist developer. In an embodiment, a hard mask including a high-k dielectric is formed. In a further embodiment, a protection layer is formed underlying a photoresist pattern. The protection layer may protect one or more layers formed on the substrate from a photoresist stripping process.

PRIORITY DATA

This application claims priority to Provisional Application Ser. No.61/091,159 filed on Aug. 22, 2008, entitled “METHOD OF PATTERNING AMETAL GATE OF SEMICONDUCTOR DEVICE”, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

The present disclosure relates generally an integrated circuit deviceand, more particularly, a method of patterning a gate structure of an ICdevice.

As technology nodes decrease, semiconductor fabrication processes haveintroduced the use of gate dielectric materials having a high dielectricconstant (e.g., high-k dielectrics). The high-k dielectrics exhibit ahigher dielectric constant than the traditionally used silicon dioxidewhich allows for thicker dielectric layers to be used to obtain similarequivalent oxide thicknesses (EOTs). The processes also benefit from theintroduction of metal gate structures providing a lower resistance thanthe traditional polysilicon gate structures.

However, the fabrication processes providing for use of a high-kdielectric plus metal gate structure face challenges. For example,problems arise in using conventional photolithography techniques topattern high-k metal gate structures. Traditional methods to removemasking elements (e.g., dry ash and wet etch processes to removephotoresist) may damage the underlying high-k gate dielectric filmand/or the metal gate films. Furthermore, the formation of a photoresistfeature directly on a metal film which is to be patterned may raisechallenges. For example, photoresist peeling may occur due to pooradhesion between the photoresist and metal.

Therefore, what is needed is an improved method of patterning a metalgate structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating an embodiment of a method of forminga gate structure using a soluble hard mask.

FIGS. 2, 3, 4 a, 4 b, 5, and 6 are cross-sectional views of asemiconductor device corresponding to the steps of an embodiment of themethod of FIG. 1.

FIG. 7 is a flowchart illustrating an embodiment of a method of forminga gate structure using a high-k dielectric hard mask.

FIGS. 8-11 are cross-sectional views of a semiconductor devicecorresponding to steps of an embodiment of the method of FIG. 7.

FIG. 12 is a flowchart illustrating an alternative embodiment of amethod of forming a gate structure using a protection layer.

FIGS. 13-17 are cross-sectional views of a semiconductor devicecorresponding to steps of an embodiment of the method of FIG. 7.

DETAILED DESCRIPTION

The present disclosure relates generally to forming an integratedcircuit device and, more particularly, to patterning a metal gatestructure of a semiconductor device (e.g., a FET device of an integratedcircuit). It is understood, however, that the following disclosureprovides many different embodiments, or examples, for implementingdifferent features of the invention. Specific examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition is forthe purpose of simplicity and clarity and does not in itself dictate arelationship between the various embodiments and/or configurationsdiscussed. Furthermore, included are descriptions of a first layer orfeature “on” or “overlying” (as well as similar descriptions) a secondlayer or feature. These terms include embodiments where the first andsecond layer are in direct contact and those where one or more layers orfeature are interposing the first and second layer. Further still, theexemplary embodiments are for illustrative purposes and not intended tobe limiting, for example, numerous configurations of high-k metal gatestructures are known in the art, including layers which may or may notbe distinctly described herein but would be readily recognizable by oneskilled in the art.

Referring to FIG. 1, illustrated is a flowchart providing an embodimentof a method 100 of forming a gate structure. FIGS. 2, 3, 4 a, 4 b, 5,and 6 provide exemplary devices corresponding to the fabrication stepsof the method 100. The method 100 may be included during processing ofan integrated circuit, or portion thereof, that may comprise staticrandom access memory (SRAM) and/or other logic circuits, passivecomponents such as resistors, capacitors, and inductors, and activecomponents such as P-channel field effect transistors (PFET), N-channelFET (NFET), metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolartransistors, high voltage transistors, high frequency transistors, othermemory cells, combinations thereof, and/or other semiconductor devices.

The method 100 begins at step 102 where a substrate (e.g., wafer) isprovided. In the example of FIG. 2, a substrate 202 is provided. In anembodiment, the substrate 202 includes a silicon substrate incrystalline structure. The substrate 202 may include various dopingconfigurations depending on design requirements as is known in the art(e.g., p-type substrate or n-type substrate) Other examples of thesubstrate 202 include other elementary semiconductors such as germaniumand diamond. Alternatively, the substrate 202 may include a compoundsemiconductor such as, silicon carbide, gallium arsenide, indiumarsenide, or indium phosphide. Further, the substrate 202 may optionallyinclude an epitaxial layer (epi layer), may be strained for performanceenhancement, and/or may include a silicon-on-insulator (SOI) structure.Further still, the substrate 202 may include a plurality of featuresformed thereon, including active regions, source and drain regions inthe active regions, isolation regions (e.g., shallow trench isolation(STI) features), and/or other features known in the art. The STI feature204 is formed on the substrate 202 separating (e.g., isolating) a firstactive region 206 and a second active region 208. The STI feature 204formed in the substrate 202. The STI feature 204 may include siliconoxide, silicon nitride, silicon oxynitride, fluoride-doped silicateglass (FSG), and/or a low-k dielectric material. Other isolation methodsand/or features are possible in lieu of or in addition to STI. The STIfeature 204 may be formed using processes such as reactive ion etch(RIE) of the substrate 202 to form a trench which is filled withinsulator material using deposition processes known in the art, followedby CMP processing. In an embodiment, the first active region 206includes a portion of the substrate 202 in which a PMOS device will beformed; the second active region 208 includes a portion of the substrate202 in which an NMOS device will be formed, though any configuration ispossible.

In the exemplary embodiment of FIG. 2, a gate dielectric layer 210 and acapping layer 212 are formed on the substrate 202. However, numerousconfigurations are possible. The gate dielectric layer 210 may includean interface layer and a high-k gate dielectric layer. The interfacelayer may include silicon, oxygen, and/or nitrogen. In an embodiment,the interface layer is SiO₂. The interface layer may include a thicknessof approximately 6 to 8 angstroms, though various other thicknesses maybe suitable. The interface layer may be formed by atomic layerdeposition (ALD) and/or other suitable processes. In an embodiment, gatedielectric layer 210 includes a high-k (high dielectric constant)material. The high-k dielectric material includes hafnium oxide (HfO₂).Other examples of high-k dielectrics include hafnium silicon oxide(HfSiO), hafnium silicon oxynitride (HfSiON), hafnium tantalum oxide(HfTaO), hafnium titanium oxide (HfTiO), hafnium zirconium oxide(HfZrO), combinations thereof, and/or other suitable materials. The highk-gate dielectric layer 210 may be formed by ALD, chemical vapordeposition (CVD), and/or other suitable processes. In an embodiment, thethickness of the high-k gate dielectric is between approximately 10 and30 angstroms (A).

The capping layer 212 may include a work function dielectric for tuninga work function of a metal layer (e.g., providing the metal gateelectrode). The tuning of the work function may allow for the metal gateto properly function as part of an NMOS or PMOS transistor device. Thecapping layer 212 may include aluminum or lanthanium based-dielectrics,and/or other suitable compositions. In an embodiment, the interfacelayer and/or the capping layer 212 may be omitted, and/or other suitablelayers may be included on the substrate 202.

The method 100 then proceeds to step 104 where a metal layer is formedon the substrate. The metal layer may be such that, when patterned itforms a metal gate electrode, or portion thereof. In an embodiment, themetal layer includes a work function metal such that it provides anN-metal work function or P-metal work function of a metal gate.Referring to the example of FIG. 2, a metal layer 214 is formed on thesubstrate 202. The metal layer 214 may include one or more layersincluding Ti, TiN, TaN, Ta, TaC, TaSiN, W, WN, MoN, MoON, RuO₂, and/orother suitable materials. The metal layer 214 may include one or morelayers formed by physical vapor deposition (PVD), CVD, ALD, plating,and/or other suitable processes. Examples of work function metals thatmay be included in the metal layer 214 include p-type work functionmetal materials and n-type work function metal materials. P-type workfunction materials include compositions such as ruthenium, palladium,platinum, cobalt, nickel, and conductive metal oxides, and/or othersuitable materials. N-type metal materials include compositions such ashafnium, zirconium, titanium, tantalum, aluminum, metal carbides (e.g.,hafnium carbide, zirconium carbide, titanium carbide, aluminum carbide),aluminides, and/or other suitable materials.

The method 100 then proceeds to step 106 where a hard mask layer isformed on the substrate, overlying the metal layer, described above withreference to step 104. The hard mask layer includes a composition suchthat it is soluble and thus, removable from the substrate. The hard masklayer may be soluble in at least one of water, low concentration acid,or a base solution such as, a developer. The solubility of the hard maskallows it to be removed in-situ with (e.g., a substantially the sametime as) a photoresist layer, such as described below with reference tostep 110. The hard mask layer may be formed by physical vapordeposition, chemical vapor deposition, and/or other suitable processes.The hard mask layer may include a thickness between approximately 10 and30 A. In an embodiment, the hard mask layer is 20 A. The hard mask layermay include a single layer or a multiple layer structure. Referring tothe example of FIG. 2, a hard mask layer 216 is formed. The compositionof the hard mask layer 216 may be such that it is removed by water, aweak acid, a base solution such as, a photoresist developer, and/orcombinations thereof. The hard mask layer 216 may include a plurality oflayers.

In an embodiment, the hard mask layer 216 includes a dielectriccomposition that is removable by water. Examples of suitablecompositions include La containing dielectrics such as, La₂O₃. In anembodiment, the hard mask layer 216 includes a dielectric compositionthat is removable by a base solution. The base solution may includephotoresist developers known in the art, including, for example,tetra-methyl-ammonium-hydroxide (TMAH) photoresist developer solution.Examples of suitable dielectrics include Al containing dielectrics suchas, Al₂O₃.

The method 100 then proceeds to step 108 where a photoresist layer isformed on the hard mask. The photoresist layer may be spun-on and/ordeposited by other suitable methods. Though illustrated herein as apositive tone resist, use of a negative resist is also possible.Referring to the example of FIG. 2, the photoresist layer 218 is formed.

The method 100 then proceeds to step 110 where the photoresist layer andthe hard mask layer are patterned. The photoresist layer is patternedusing suitable processes known in the art. For example, referring to theexample of FIG. 2, the photoresist layer 218 is exposed to a pattern bya passing a radiation beam 220 through a photomask. The radiation beam220 may be ultraviolet and/or can be extended to include other radiationbeams such as ion beam, x-ray, extreme ultraviolet, deep ultraviolet,and other proper radiation energy. A post-exposure bake (PEB) istypically performed to allow the exposed photoresist polymers to cleave.The substrate including the cleaved polymer photoresist is thentransferred to a developing chamber to remove the exposed photoresist,which is soluble to an aqueous developer solution. Typically, adeveloper solution such as tetra-methyl ammonium hydroxide (TMAH) isapplied to the resist surface in the form of a puddle to develop theexposed photoresist. A de-ionized (DI) water rinse may then applied tothe substrate to remove the dissolved polymers of the photoresist. Adrying process (e.g., a spin dry process) may follow.

The hard mask 216 may also be patterned substantially simultaneously to(e.g., serially within the same process) and/or in-situ with thefabrication of the photoresist pattern. In an embodiment, the hard mask216 is removable by a base solution (e.g., a developer). In theembodiment, as the developer is applied to the photoresist 218, theexposed portion of the photoresist is removed by the developer, exposing(e.g., opening) a portion of the underlying hard mask layer 216. Thehard mask 216 being removable (e.g., soluble) in the developer isremoved from the substrate—in the portions contacting the developer(e.g., underlying the soluble photoresist 218 a). Thus, referring to theexample of FIG. 3, the device 300 is provided including the patternedphotoresist 304 and the patterned hard mask 302.

In an embodiment, the hard mask 216 is removable by water. In theembodiment, an exposed portion of the photoresist 218 a is removed bythe development process, thus exposing (e.g., opening) a portion of theunderlying hard mask layer 216. A rinse may follow the developmentprocess and/or the development process itself may include water. Thehard mask 216 being removable (e.g., soluble) in water is then removedfrom the substrate 202—in the portions not protected by the remainingphotoresist pattern (e.g., underlying the soluble photoresist 218 a).Thus, also referring to the example of FIG. 3, the device 300 isprovided including the patterned photoresist 304 and the patterned hardmask 302.

The method 100 then proceeds to step 112 where the metal layer ispatterned. The metal layer may be patterned to form a metal gate. In anembodiment, the metal layer includes a work function metal. One or morelayers underlying the metal layer may also be patterned.

In an embodiment, the patterned photoresist and the patterned hard maskprovide a masking element used to pattern the metal layer. Such anembodiment, is illustrated in the example of FIG. 4 a. The metal gate402 (formed of the metal layer 214) and patterned capping layer 404(formed of the capping layer 212) are formed using a masking elementincluding the photoresist pattern 304 and the hard mask layer 302. Themethod 100 then proceeds to step 114 where the photoresist is removedfrom the substrate. Referring to the example of FIG. 5, the photoresistis removed and the patterned hard mask 302, metal gate 402 and patternedcapping layer 404 are disposed on the substrate 202. In an embodiment,the underlying gate dielectric layer 210 may also be patterned.

In an alternative embodiment of the method 100, in step 112, thepatterned photoresist is removed, and the patterned hard mask provides amasking element used to pattern the metal layer. Such an embodiment isillustrated in the example of FIG. 4 b. The photoresist 304 has beenremoved from the substrate 202 and the patterned hard mask 302 remainsand is used as a masking element to remove portions of the metal layer214. Referring to FIG. 5, the patterned hard mask 302 is used as amasking element to provide the patterned metal gate 402 and patternedcapping layer 404 disposed on the substrate 202. In an embodiment, theunderlying gate dielectric layer 210 may also be patterned.

The method 100 then proceeds to step 116 where the hard mask is removedfrom the substrate. The hard mask may be removed by wet etching, dryetching, plasma processes, chemical mechanical polish (CMP), and/orother suitable processes. In an embodiment, the hard mask includes awater soluble composition (e.g., La₂O₃) and may be removed by a waterrinse. In an embodiment, the hard mask includes a base solution-solublematerial (e.g., Al₂O₃) and may be removed by a base solution such as, adeveloper (e.g., TMAH).

Referring to the example of FIG. 6, the hard mask 302 is removed toprovide the device 600 including the substrate 202 having the gatedielectric layer 210, the patterned capping layer 404 and the patternedmetal gate 402. In an embodiment, the gate dielectric layer 210 is alsopatterned (e.g., removed from the second active region 208). The metalgate 402 provides a metal gate electrode, or portion thereof, of atransistor in the active region 206 of the substrate 202. In anembodiment, the metal gate 402 provides a metal gate of an NMOStransistor, while the metal layer (e.g., metal layer 214) is remove fromthe active region 204 (e.g., where a PMOS transistor may be formed).

The method 100 may continue to include processes that form a metal gateon the region 208 of the substrate (e.g., a PMOS transistor metal gate).In an embodiment, a second metal layer, for example, a P-metal workfunction layer is formed on the substrate. The second metal layer may beconformally deposited over the substrate 202 including overlying themetal gate 402. A chemical mechanical polish (CMP) process may be usedto reduce and/or eliminate the second metal layer overlying the metalgate 402. In an embodiment, a thin portion of the second metal layer mayremain over the metal gate 402, but minimally effect the work functionof the metal gate 402. Alternatively, the CMP process may planarize thesecond metal layer such that the top surface of the second metal layeris co-linear with the top surface of the metal gate 402, the secondmetal layer being present only in the active area 208. In an embodiment,photolithography processes, such as those described above, may be usedto form a second metal gate in the active area 208.

The method 100 may be included in a “gate first” or “gate last”fabrication process. In a gate last process, a dummy gate structure(e.g., a sacrificial polysilicon gate) may be formed over a gatedielectric and/or the work function metal layer. The dummy gatestructure is then removed to form a trench within which a gate electrodeor portion thereof may be formed.

The method 100 may provide benefits over conventional processes such as,improved adhesion of a photoresist layer. Forming a photoresist layerdirectly on the metal layer may provide for poor adhesion of thephotoresist to the metal leading to issues such as photoresist peeling.In contrast, formation of the photoresist of the method 100 on a hardmask layer may provide improved adhesion. Furthermore, use ofconventional hard masks may cause issues with removal of the hard mask,for example, metal gate oxidation, high-k dielectric and/or metal gatedamage, and/or other issues. One or more of these issues may be improvedby the use of a soluble-hard mask.

Referring now to FIG. 7, illustrated is a method 700 for patterning of agate structure. The method 700 may be used to form a metal gatestructure having a high-k dielectric. FIGS. 8-11 provide exemplaryembodiments of a semiconductor device according to the fabrication stepsof the method 700. The method begins at step 702 where a substrate isprovided. Referring to the example of FIG. 8, the substrate 802 isprovided. The substrate 802 may be substantially similar to thesubstrate 202 described above with reference to FIG. 2. The STIstructure 804 may be substantially similar to the STI structure 204,also described above with reference to FIG. 2, and isolates two activeregions of the substrate 202, region 806 and 808.

The method 700 then proceeds to step 704 where a gate dielectric layeris formed on the substrate. The gate dielectric layer may include ahigh-k dielectric material. Referring to the example of FIG. 8, thehigh-k gate dielectric layer 810 is formed on the substrate 802. Thehigh-gate dielectric layer 810 may be substantially similar to gatedielectric layer 210, described above with reference to FIG. 2. In anembodiment, an interface layer is formed underlying the high-k gatedielectric layer. The interface layer may include a thickness between 5and 10 Angstroms. The interface layer may include silicon, oxygen,nitride, and/or other suitable materials. In an embodiment, theinterface layer includes SiO₂.

The method 700 then proceeds to step 706 where a metal layer is formedon the substrate. The metal layer may be used form a metal gate, orportion thereof. In an embodiment, the metal layer includes p or n-workfunction metal. Referring to the example of FIG. 8, the metal layer 812is formed. The metal layer 812 may be substantially similar to the metallayer 214 described above with reference to FIG. 2. For example, themetal layer 812 may include a plurality of metal layers one or more ofwhich is used in forming a metal gate.

The method 700 then proceeds to step 708 where a hard mask layer isformed on the substrate. The hard mask layer may be a single layer ormultiple layer feature. The hard mask layer includes a high-k dielectricmaterial. Examples of high-k dielectrics include hafnium oxide (HfO₂),hafnium silicon oxide (HfSiO), hafnium silicon oxynitride (HfSiON),hafnium tantalum oxide (HfTaO), hafnium titanium oxide (HfTiO), hafniumzirconium oxide (HfZrO), combinations thereof, and/or other suitablematerials. The hard mask layer may be formed by ALD, CVD, and/or othersuitable processes. The hard mask layer may include the same compositionas the gate dielectric, described above with reference to step 704, or adifferent composition. In an embodiment, the composition of the hardmask layer and the gate dielectric are selected such that they providedifferent etch rates. Referring to the example of FIG. 8, the hard masklayer 814 is formed. The hard mask layer 814 includes a high-kdielectric material. In an embodiment, the hard mask layer 814 includesa thickness of approximately 12 Angstroms. The hard mask layer 814 maybe substantially the same thickness as the gate dielectric layer 810.

The method 700 then proceeds to step 710 where a patterned photoresistlayer is formed on the substrate. A photoresist layer may be spun-onand/or deposited by other suitable methods. The resist may be positiveor negative tone. The photoresist layer is patterned using suitableprocesses known in the art. For example, the photoresist layer isexposed to a pattern by a passing a radiation beam through a photomask.The radiation beam may be ultraviolet and/or can be extended to includeother radiation beams such as ion beam, x-ray, extreme ultraviolet, deepultraviolet, and other proper radiation energy. A post-exposure bake(PEB) is typically performed to allow the exposed photoresist polymersto cleave. The substrate including the cleaved polymer photoresist isthen transferred to a developing chamber to remove the exposedphotoresist, which is soluble to an aqueous developer solution.Typically, a developer solution such as tetra-methyl ammonium hydroxide(TMAH) is applied to the resist surface in the form of a puddle todevelop the exposed photoresist. A de-ionized (DI) water rinse may thenapplied to the substrate to remove the dissolved polymers of thephotoresist. A drying process (e.g., a spin dry process) may follow.Referring to the example of FIG. 8, the photoresist pattern 816 isformed. The photoresist pattern 816 may define a pattern providing for ametal gate (e.g., metal gate electrode).

The method 700 then proceeds to step 712 where the hard mask layer ispatterned. The hard mask layer may be patterned using the photoresistpattern, described above with reference to step 710, as a maskingelement. Referring to the example of FIG. 9, the patterned hard masklayer 902 is formed.

The method 700 then proceeds to step 714 where the metal layer ispatterned. In an embodiment, the metal layer is patterned in-situ andsubstantially simultaneously with the patterning of the hard mask. Themetal layer may be patterned (e.g., etched) using a masking elementincluding the photoresist pattern. The metal layer may be removed usinga wet etch, dry etch, plasma, and/or other suitable processes. Referringto the example of FIG. 9, the metal gate 904 is provided (by patterningthe metal layer 812).

The method 700 then proceeds to step 716 where the photoresist patternis removed from the substrate. The photoresist may be removed (e.g.,stripped) from the substrate using wet etch, dry etch, dry ash, and/orother suitable processes. Referring to the example of FIG. 10, thephotoresist pattern is removed from the substrate 802 providing a gatedielectric layer 810, metal gate 904, and overlying patterned hard mask902.

The method 700 then proceeds to step 716 where the hard mask is removed.In an embodiment, the gate dielectric layer not underlying the metalgate is also removed. The hard mask and/or gate dielectric layer may beremoved using wet etch, dry etch, plasma, and/or other suitabletreatments. The hard mask and gate dielectric may be removed atsubstantially the same rate (for example, if they comprise similarhigh-k dielectric compositions). In other embodiments, the hard mask maybe removed and the gate dielectric layer may remain on the substrate. Inan embodiment, the gate dielectric layer may be partially removed, forexample, decreasing in thickness. In such an example, the gatedielectric layer may include a first thickness underlying the metal gateand provide a second thickness (e.g., less than the first thickness), inthe open area of the substrate.

Referring to the example of FIG. 11, the hard mask 902 is removed andthe gate dielectric 810 is removed to provide the patterned gatedielectric layer 1102 underlying the metal gate 904. The gate dielectriclayer has been removed from the exposed (e.g, open) areas of thesubstrate including the region 808. In an embodiment, the region 806provides an active area for formation of a PMOS or NMOS device includingthe metal gate 904, and the region 808 provides an active area forformation of the other of a PMOS or NMOS device.

The method 700 may continue to include processes that form a metal gateon the region 708 of the substrate (e.g., a PMOS transistor metal gate).In an embodiment, a second metal layer, for example, an N- or P-metalwork function layer is formed on the substrate. The second metal layermay be conformally deposited over the substrate 702 including overlyingthe metal gate 402. A chemical mechanical polish (CMP) process may beused to reduce and/or eliminate the second metal layer overlying themetal gate 904. In an embodiment, a thin portion of the second metallayer may remain over the metal gate 904, but minimally effect the workfunction of the metal gate 904. Alternatively, the CMP process mayplanarize the second metal layer such that the top surface of the secondmetal layer forming the second gate is co-linear with the top surface ofthe metal gate 904, the second metal layer being present only in theactive area 808. In an embodiment, photolithography processes, such asthose described above, may be used to form a second metal gate in theactive area 808. Underlying the second metal layer, a gate dielectriclayer may be formed, or as described above in step 716 the gatedielectric layer (e.g, gate dielectric layer 810) may remain on thesubstrate in whole or in part, as the hard mask is selectively removed.

The method 700 may be included in a “gate first” or “gate last”fabrication process. In a gate last process, a dummy gate structure(e.g., a sacrificial polysilicon gate) may be formed over a gatedielectric. The dummy gate structure is then removed to form a trenchwithin which a gate electrode may be formed.

The method 700 may provide benefits over conventional processes such as,improved adhesion of a photoresist layer. For example, adhesion ofphotoresist and a high-k dielectric hard mask may be greater than thatbetween photoresist and a metal layer that is to patterned. Theincreased adhesion may provide for decreased instances of photoresistpeeling (e.g., during wet processes). Further advantages may be seen byreduction of damage to the high-k gate dielectric and/or metal gate thatmay be caused by conventional dry ash and/or wet etch removal of aphotoresist layer and/or hard mask.

Referring now to FIG. 12, illustrated is a method 1200 for fabricating agate structure. FIGS. 13-17 illustrate exemplary embodiments of a devicecorresponding to the steps of the method 1200. The method 1200 begins atstep 1202 where a substrate is provided. Referring to the example ofFIG. 13, a substrate 1302 is provided. The substrate 1302 may besubstantially similar to the substrate 202 described above withreference to FIG. 2. The substrate 1302 includes a shallow trenchisolation feature 1304 that isolates regions of the substrate 1302, suchas a PMOS region and an NMOS region. The substrate 1302 includes a gatedielectric film 1310 and a metal layer 1312. Examples of suitable metalsto be including the metal layer 1312 include TaN, TaSiN, W, TaC, TaCN,TiAlN, Al, TiN, and/or other suitable materials. In an embodiment, themetal layer 1312 has a thickness between approximately 10 A and 200 A.The gate dielectric film 1310 may be a high-k dielectric materialincluding, for example, HfO₂, HfSiO, HfSiON, HfZrO, and/or othersuitable materials. The gate dielectric film 1310 may be substantiallysimilar to the gate dielectric layer 210, described above with referenceto FIG. 2. In an embodiment, the gate dielectric film 1310 has athickness between approximately 10 and 30 Angstroms.

The method 1200 then proceeds to step 1204 where a metal gate layer isformed on the substrate. The metal gate electrode layer may include ap-metal or n-metal composition and provide the work function of a metalgate. Referring to the example of FIG. 13, the metal gate layer 1314 isformed. The metal gate layer 314 may be substantially similar to themetal layer 214, described above with reference to FIG. 2. In anembodiment, the metal layer 1314 has a thickness between approximately10 and 200 Angstroms. The metal layer 1314 may include one or morelayers that provide a metal gate electrode or portion thereof.

The method 1200 then proceeds to step 1206 where a protection layer isformed on the substrate, overlying the metal layer. In an embodiment,the protection layer includes an oxide. Examples of suitable oxidesinclude spin-on glass (SOG), teraethoxysilane (TEOS), PE-oxide (oxideformed by plasma enhanced processes, e.g., CVD), HARP oxide (e.g., densethermally grown oxide), and/or other possible oxide materials. In anembodiment, the protection layer includes silicon. Examples of siliconcompositions include polysilicon, amorphous silicon, and/or othersuitable compositions. Referring to the example of FIG. 13, theprotection layer 1316 is formed. In an embodiment, the protection layer1316 has a thickness between approximately 100 and 200 Angstroms.

The method 1200 then proceeds to step 1208 where a patterned photoresistlayer is formed on the protection layer. A photoresist layer may bespun-on and/or deposited by other suitable methods. The photoresist maybe positive tone or negative tone resist. The formed photoresist layeris patterned using suitable processes known in the art. For example, thephotoresist layer is exposed to a pattern by a passing a radiation beamthrough a photomask. The radiation beam may be ultraviolet and/or can beextended to include other radiation beams such as ion beam, x-ray,extreme ultraviolet, deep ultraviolet, and other proper radiationenergy. A post-exposure bake (PEB) is typically performed to allow theexposed photoresist polymers to cleave. The substrate including thecleaved polymer photoresist is then transferred to a developing chamberto remove the exposed photoresist, which is soluble to an aqueousdeveloper solution. Typically, a developer solution such as tetra-methylammonium hydroxide (TMAH) is applied to the resist surface in the formof a puddle to develop the exposed photoresist. A de-ionized (DI) waterrinse may then applied to the substrate to remove the dissolved polymersof the photoresist. A drying process (e.g., a spin dry process) mayfollow. Referring to the example of FIG. 13, the patterned photoresist1318 is formed. The patterned photoresist 1318 may provide a patternassociated with formation of a metal gate.

The method 1200 then proceeds to step 1210 where the protection layer ispatterned using the patterned photoresist as a masking element. Theprotection layer may be patterned such a portion of the protection layeris removed from unmasked (e.g., open area) of the substrate. Thisprovides a thin layer of protection layer remaining on the open areas(e.g., those not underlying the patterned photoresist, described abovewith reference to step 1212). The protection layer may be patternedusing a wet etch. Other processes may be used to remove (pattern) theprotection layer such as, dry etch, plasma etch, and/or other suitablemethods. Referring to the example of FIG. 14, the patterned protectionlayer 1402 is provided. The patterned protection layer 1402 includes athin layer of material overlying the open area of the substrate 1302,including over the active region 1306. The patterned protection layer1402 has a first thickness tp1 underlying the patterned photoresist 1318and a second thickness tp2 in the open area (e.g., unmasked) of thesubstrate 1302. In an embodiment, tp1 is a thickness betweenapproximately 100 and 2000 Angstroms. In an embodiment, tp2 is athickness between approximately 20 and 200 Angstroms. In a furtherembodiment, tp2 is a thickness between approximately 30 and 50Angstroms.

The method 1200 then proceeds to step 1212 where the photoresist andunmasked, patterned protection layer are removed. The removal mayinclude a wet etch process, such as, a wet etch including sulfuricacid-hydrogen peroxide solution (SPM) and/or a diluted hydrofluoric acid(DHF) (e.g., 1:50 to 1:1000 concentration). In an embodiment, a SPMprocess is followed by a DHF process. The SPM process may be between 30seconds and 3 minutes, the DHF process may be between 10 seconds and 3minutes, though numerous other embodiments are possible. A SPM and/orDHF process may be beneficial to provide removal of a protective filmcomprising an oxide. In an embodiment, a wet etch including SPM andNH₄OH or TMAH is provided. This etch chemistry may provide for removalof a protection layer including a silicon layer (e.g., polysilicon oramorphous silicon). Referring to the example of FIG. 15, the patternedphotoresist 1318 and the portion of the patterned protection layer 1402not masked by the photoresist pattern 1318 has been removed, leaving theprotection layer masking element 1502. The masking element 1502 mayprovide a masking element to pattern the metal layer 1314 to form ametal gate, or portion thereof, on the active region 1304.

The method 1200 then proceeds to step 1214 where the metal layer ispatterned using the protection layer as a masking element. The metallayer may be patterned to form a metal gate (e.g., metal gate electrode)or portion thereof. The metal layer may be patterned using process suchas wet etch, dry etch, plasma processes, and/or other suitableprocesses. In an embodiment, the metal layer is patterned using anammonia hydroxide-hydrogen peroxide mixture (APM). Referring to theexample of FIG. 16, the metal gate 1602 is formed. The metal gate 1602may include a portion of metal gate (e.g., work function) for an NMOS orPMOS transistor formed in the region 1304 of the substrate 1302. In anembodiment, one or more of the underlying layers, such as the bufferlayer 1312 and/or the gate dielectric layer 1310 are also patterned.

The method 1200 then proceeds to step 1216 where the remainingprotection layer (e.g., patterned protection layer) is removed from thesubstrate. The protection layer may be removed using wet etch, dry etch,CMP, plasma, and/or other suitable processes. In an embodiment, theprotection layer is removed using a wet etch process including dilutedhydrofluoric acid (DHF). Referring to the example of FIGS. 16 and 17,the patterned protection layer 1502 is removed and the device 1700 isformed.

The method 1200 may continue to include processes that form a metal gateon the region 1306 of the substrate. In an embodiment, a second metallayer, for example, an N or P-metal work function layer is formed on thesubstrate. The second metal layer may be conformally deposited over thesubstrate 1302 including overlying the metal gate 1602. A chemicalmechanical polish (CMP) process may be used to reduce and/or eliminatethe second metal layer overlying the metal gate 1602. In an embodiment,a thin portion of the second metal layer may remain over the metal gate1602, but minimally effect the work function of the metal gate 1602.Alternatively, the CMP process may planarize the second metal layer suchthat the top surface of the second metal layer (the second metal gate)is co-linear with the top surface of the metal gate 1602, the secondmetal layer being present only in the active area 1306. In anembodiment, photolithography processes, such as those described above,may be used to form a second metal gate in the active area 1306.

The method 1200 may be included in a “gate first” or “gate last”fabrication process. In a gate last process, a dummy gate structure(e.g., a sacrificial polysilicon gate) may be formed over a gatedielectric. The dummy gate structure is then removed to form a trenchwithin which a gate electrode may be formed.

The method 1200 may provide benefits over conventional processes suchas, improved adhesion of a photoresist layer. For example, adhesion ofphotoresist and a protection layer may be greater than that betweenphotoresist and a metal layer that is to patterned. The increasedadhesion may provide for decreased instances of photoresist peeling(e.g., during wet etch processes). Further advantages may be seen byreduction of damage to the high-k gate dielectric and/or metal gate thatmay be caused by conventional dry ash and/or wet etch removal of aphotoresist layer. The protection layer, for example, including theprotection layer of thickness tp2 overlying the region 1306 of thesubstrate, may protect the high-k dielectric 1312 and/or the metal layer1314 from a process used to strip the photoresist 1318.

While the preceding description shows and describes one or moreembodiments, it will be understood by those skilled in the art thatvarious changes in form and detail may be made therein without departingfrom the spirit and scope of the present disclosure. Therefore, theclaims should be interpreted in a broad manner, consistent with thepresent disclosure.

1. A method of fabricating a semiconductor device, comprising: forming ametal layer on a semiconductor substrate; forming a soluble hard masklayer on the metal layer, wherein the soluble hard mask layer is solublein at least one of water and a developer; patterning the hard mask layerto form a masking element; and using the masking element to pattern themetal layer to form at least a portion of a metal gate.
 2. The method ofclaim 1, wherein the patterning the hard mask is in-situ with thepatterning of an overlying photoresist layer.
 3. The method of claim 1,wherein the patterning the hard mask includes removing a portion of thehard mask using water.
 4. The method of claim 1, wherein the patterningthe hard mask includes removing a portion of the hard mask using aphotoresist developer.
 5. The method of claim 4, wherein the photoresistdeveloper includes TMAH.
 6. The method of claim 1, further comprising:depositing a photoresist layer on the hard mask; exposing thephotoresist layer; and applying a developer to the exposed photoresistlayer, wherein the developer removes the exposed photoresist layer and aportion of the hard mask underlying the exposed photoresist layer. 7.The method of claim 1, further comprising: forming a high-k gatedielectric layer under the metal layer.
 8. A method of fabricating agate structure, comprising: forming a gate dielectric layer on asemiconductor substrate, wherein the gate dielectric includes a firsthigh-k dielectric; forming a metal layer on the high-k gate dielectriclayer; forming a hard mask layer on the metal layer, wherein the hardmask layer includes a second high-k dielectric; patterning the hard masklayer and the metal layer wherein the patterning defines a first portionand a second portion of the gate dielectric layer, wherein the firstportion underlies the hard mask and the second portion is in an openarea of the substrate; and removing the hard mask layer and the secondportion of the gate dielectric layer.
 9. The method of claim 8, whereinthe first and second high-k dielectric are substantially similar. 10.The method of claim 8, wherein the first and second high-k dielectricshave different etch rates.
 11. The method of claim 8, wherein thepatterning the metal layer includes forming at least a portion of ametal gate.
 12. The method of claim 8, further comprising: depositing aphotoresist layer on the hard mask; patterning the photoresist layer toform a photoresist masking element, wherein the patterning the hard maskand metal layer includes using the photoresist masking element; andstripping the photoresist masking element prior to removing the hardmask.
 13. The method of claim 8, wherein the second high-dielectric isselected from the group consisting of hafnium oxide (HfO₂), hafniumsilicon oxide (HfSiO), hafnium silicon oxynitride (HfSiON), hafniumtantalum oxide (HfTaO), hafnium titanium oxide (HfTiO), hafniumzirconium oxide (HfZrO), and combinations thereof.
 14. A method offabricating a semiconductor device, comprising: forming a metal layer ona semiconductor substrate; forming a protection layer on the metallayer; removing a portion of the protection layer to provide a firstregion having a first thickness and a second region having a secondthickness, wherein the first region is underlying a photoresist maskingelement; removing the photoresist masking element; removing the secondregion of the protection layer from the substrate after removing thephotoresist masking element; and patterning the metal layer using thefirst region of the protection layer.
 15. The method of claim 14,wherein the second thickness is approximately 30 and 50 Angstroms. 16.The method of claim 14, wherein the patterning the metal layer includesforming at least a portion of a metal gate.
 17. A method of claim 14,further comprising: depositing a high-k dielectric layer on thesemiconductor substrate underlying the metal layer.
 18. The method ofclaim 14, wherein the protection layer includes an oxide.
 19. The methodof claim 18, wherein the protection layer is selected from the groupconsisting of: include spin-on glass (SOG), teraethoxysilane (TEOS),PE-oxide, and HARP oxide.
 20. The method of claim 14, wherein theprotection layer includes silicon.